The present invention relates to drafting apparatus and particularly to a drawing board and an associated T-square means of novel construction. A T-square comprises a head portion having an edge adapted to slide along a side edge of a drafting board and a blade portion secured to the head portion in fixed 90.degree. relation and overlies the drafting board surface to facilitate the drawing of straight lines. The relationship of the T-square to the drawing board is very important to the draftsman to facilitate his work.
Prior proposed T-square and drafting board combinations have included the use of magnet means on the T-square head portion to facilitate retention of the T-square in a selected position. In such prior proposed construction, the edge of the board was provided with a strip of magnet material and the head portion of the T-square had mounted thereon magnets in different arrangements and cooperable with the strip of magnetic material. One such prior construction is shown in U.S. Pat. No. 1,245,821. In British Pat. No. 768,399, published Feb. 13, 1957, an eccentric was provided in the T-square head portion to provide a variable air gap between the magnet and the armature to vary the holding power of the magnets. Another prior magnetic T-square construction is shown in U.S. Pat. No. 1,642,232. In U.S. Pat. No. 3,137,072 a T-square is provided with horseshoe magnets arranged around rollers which engage the side edge of a drawing board provided with an armature strip. In such prior proposed constructions, the armature strip and the magnet means cooperated in expected manner for holding and stabilizing the relationship of the T-square with respect to the drawing board.
Further, combinations of T-square and drawing boards known to me always required that the side edge of the drawing board be used as the guide surface for the head portion of the T-square.